linux-kernel - Re: [RFC PATCH] vfio/pci: add PCIe TPH to device feature ioctl

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Message-ID: <20250401235225.GA327284@ziepe.ca>
Date: Tue, 1 Apr 2025 20:52:25 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Wathsala Wathawana Vithanage <wathsala.vithanage@....com>
Cc: "Tian, Kevin" <kevin.tian@...el.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	nd <nd@....com>, Philipp Stanner <pstanner@...hat.com>,
	Yunxiang Li <Yunxiang.Li@....com>,
	"Dr. David Alan Gilbert" <linux@...blig.org>,
	Ankit Agrawal <ankita@...dia.com>,
	"open list:VFIO DRIVER" <kvm@...r.kernel.org>,
	Dhruv Tripathi <Dhruv.Tripathi@....com>,
	Honnappa Nagarahalli <Honnappa.Nagarahalli@....com>,
	Jeremy Linton <Jeremy.Linton@....com>
Subject: Re: [RFC PATCH] vfio/pci: add PCIe TPH to device feature ioctl

On Tue, Apr 01, 2025 at 11:38:01PM +0000, Wathsala Wathawana Vithanage wrote:

> > Really we can't block device specific mode anyhow because we can't even
> > discover it on the kernel side..
> 
> We cannot block users from writing a steering-tag to a device specific location, but
> can we use a capability to prevent users from enabling device specific mode on the device?

qemu could do that, but the vfio kernel side really shouldn't.. There
is no reason vfio userspace on bare metal couldn't use device specific
mode.

Jason